How might one analyze the phrasing and effectiveness of stanza four of Wilfred Owen's poem "Greater Love"?
Stanza four of Wilfred Owen’s poem “Greater Love” is an especially important stanza because it marks the conclusion of the poem. In this stanza, then, one might expect Owen to try to be especially emphatic and effective, so that the reader will finish reading the work with a host of memorable thoughts feelings.
Stanza four reads as follows:
Heart, you were never hot
Nor large, nor full like hearts made great with shot; 
And though your hand be pale,
Paler are all which trail
Your cross through flame and hail:
Weep, you may weep, for you may touch them not.
The address to the “Heart” in line 19 implies the emotions of romantic love. Lines 19-20 suggest (ironically) that the metaphorically warm, swollen hearts of romantic lovers can never be as literally warm or swollen as the literal hearts of soldiers, whose hearts have been penetrated by rifle shot. Here as elsewhere in his poetry, Owen vividly contrasts naïve idealistic language with the grim realities of war.
The same strategy of ironic juxtaposition continues in the ensuing line. Thus, in line 21 the speaker refers to the stereotypically pale hands of romantic lovers – pale because they have been metaphorically drained of blood by their strong emotions. In line 22, however, the speaker once again juxtaposes such merely conventional imagery with the literal paleness of the soldiers who, wearily, must march across rugged territory.
Three words in lines 22-23 raise intriguing questions. What, precisely, does the speaker mean by the phrase “trail / Your cross”? Presumably this is an allusion to Christ, who had to drag through the streets of Jerusalem the cross on which he would be crucified. Thus the speaker seems to be associating soldiers with the virtue, humility, and self-sacrificing spirit of Jesus. The word “cross” could also suggest a trial or affliction (Oxford English Dictionary), in which case the soldiers are imagined as suffering the trials and afflictions that in some ways belong to others, who have managed to avoid them. A “cross” could also refer to a misfortune or adversity, in which case the speaker would once again be suggesting that these soldiers, Christ-like, take on themselves the suffering that belongs to others.
Some interpreters (such as Jennifer Breen in her edition of Owen’s poems) have suggested that the “cross” mentioned here may refer to soldiers’ rifles, although this suggestion seems to conflict with the verb “trail.” The clearest, least disputable allusion seems to be to Christ’s cross, dragged by him as one more burden he had to bear on his way to being crucified.
As Breen notes, the final line is clearly
an allusion to Christ’s words to Mary Magdalene after the Resurrection, when He asks her why she is weeping, and then warns her, ‘Touch me not, for I am not yet ascended to my Father’ (John 20:15-17).
The readers of the poem cannot “touch” the soldiers in several senses: they cannot have physical contact with them; they are not worthy of touching them; they may not meddle or interfere with them; they may not harm them in any way; and, especially, they may not equal them or compare with the soldiers (OED).